Mac 0SX 10.6 Importing image problems

Hi there
I have literally just started using this software so first impressions it looks very good. I have an issue though, I dont know if this is because of my lack of experience or if it's a bug in the program: I have tired importing an image but I have run into difficulties.

I click on the 'image' button at the top of the UI, this adds 'shape.png' to the screen. I click on shape.png to select it, on the right hand panel under 'object properties' I click 'select image' and browse to find my image persumably want to replace shape.png with. Nothing happens. I have tried the following formats: jpg, gif and png. I have tried saving these image initially inside or outside where the Sencha Animator project is saved. Interestingly, when I had saved the image inside my projects 'assets' project and selected it from within the program, this casued the image to dissapear from my system.

If someone could point me into the right direction that would be great.